The present invention relates to friction coupling devices that drive radiator cooling fans. A common friction coupling device is that of the dry friction drive style. Dry friction drives are used for their simplicity, cool operating temperature, and ability to turn at fully engaged peak operating speeds.
Although the present invention may be used advantageously in various configurations and applications, it is especially advantageous in a coupling device of the type used to drive a radiator cooling fan of an internal combustion engine for a over the road truck, such as a class 8 truck, and will be described in connection therewith.
Dry friction drives tend to have two operating conditions “ON and OFF”, which refers to when an associated friction clutch is either fully engaged or fully disengaged. When a friction clutch assembly is fully engaged the assembly provides cooling to an associated engine and is not slipping. When a friction clutch assembly is fully disengaged slip speed between a clutch plate and an engagement surface is at a maximum.
During the actuation of a dry friction clutch between full engagement and full disengagement the friction clutch area, referred to as the area in which there is contact between surfaces of a friction liner and a rotating shaft, generates heat or thermal energy. A certain amount of the generated thermal energy passes through the shaft to the internal clutch bearings. This passage of thermal energy to the internal bearings can degrade the bearings over time and is thus undesirable. The thermal energy transfer between the shaft and the bearings increases the operating temperature of the bearings, which in turn causes the breakdown of bearing lubricant or grease and decreases the operating efficiency and life of the bearings.
Thus, there is a need for an improved friction clutch assembly that reduces the amount of thermal energy transfer between a rotating shaft, within a friction clutch area, and internal clutch bearings. It is also desirable that the improved friction clutch assembly be similar in complexity and cost to that of traditional friction fan drive systems.